parent forum in recent topics/replies widgets

I was wondering how to modify the original widgets to be able to select “parent forum” of recent topics/replies to show in sidebar.

Example, in my forum I have forums about movies and others about literature. As website goes between those subjects, I’d like to show recent topics/replies from literature forums in the literature part of website and so in movies section.

It’s a bit mixed up to have everything in the same place, a bit confusing if you have very big forums.

I’ve been trying to add parent_forum variable into the widget with no success as it doesn’t save the data. And even if I put it manually in the db, it will not show up.